FuelLabs/fuel-core · warning

Timeout while waiting for the required fuel block height: {}

Error message

Timeout while waiting for the required fuel block height: {}

What it means

The other branch of await_block_height in the @requiredFuelBlockHeight extension: a tokio::time::sleep(timeout) races the block-height wait, and if the timeout elapses first the request fails with this message. It exists so queries requiring a specific block height do not hang forever when block production/import stalls.

Source

Thrown at crates/fuel-core/src/graphql_api/extensions/required_fuel_block_height.rs:250

    error
}

async fn await_block_height(
    block_height_subscriber: &block_height_subscription::Subscriber,
    block_height: &BlockHeight,
    timeout: &Duration,
) -> anyhow::Result<()> {
    tokio::select! {
        biased;
        block_height_res = block_height_subscriber.wait_for_block_height(*block_height) => {
            block_height_res.map_err(|e| {
                anyhow::anyhow!(
                    "Failed to wait for the required fuel block height: {}",
                    e
                )})
        },
        _ = tokio::time::sleep(*timeout) => {
            Err(anyhow::anyhow!(
                "Timeout while waiting for the required fuel block height: {}",
                block_height
            ))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::graphql_api::extensions::unify_response;
    use async_graphql::Response;
    use std::collections::BTreeMap;

    #[test]
    fn unify_response_method_is_updated() {
        // Given
        let original_error =

View on GitHub (pinned to b9d4d170da)

Solutions

1. Increase the extension's timeout so it comfortably exceeds expected block time plus import latency.
2. Check that the node is synced and importing blocks (watch block height metrics) before issuing height-pinned queries.
3. Only require heights that are recent and realistic; derive them from the node's current height, not client-side guesses.

Example fix

// before
let timeout = Duration::from_secs(5);

// after
// block time ~1s plus import/commit headroom
let timeout = Duration::from_secs(30);

// Client side: only pin a height the node can plausibly reach within the timeout.
let current = fetch_latest_height().await?;
if required_height.saturating_sub(current) as u64 * expected_block_time_secs > timeout_secs {
    return Err(anyhow::anyhow!("required height unreachable within timeout"));
}

// Server config or client: retry with backoff while the node catches up.
let mut backoff = Duration::from_millis(500);
for _ in 0..3 {
    match query_with_required_height(h).await {
        Ok(r) => return Ok(r),
        Err(e) if e.contains("Timeout while waiting for the required fuel block height") => {
            tokio::time::sleep(backoff).await;
            backoff *= 2;
            continue;
        }
        Err(e) => return Err(e),
    }
}

When it happens

Trigger: A GraphQL request requiring block N does not observe height N within the configured timeout — blocks not being produced (test/pimestamp environments), node lagging behind the network, or an unreachable/unrealistic required height.

Common situations: Timeout configured too low for the block production interval; node out of sync or stalled import pipeline; clients requiring a height far in the future; slow disk starving block import.

Understand the failure class

• Timeouts: ETIMEDOUT, deadlines, and hung requests — what actually expires when a request times out.

Related errors

• Failed to wait for the required fuel block height: {}
• {error}
• The `message_block_height` is higher than `commit_block_heig
• The count of leaves - messages is zero
• The block height subscription channel was closed: {:?}

AI-assisted analysis of FuelLabs/fuel-core@b9d4d170da (2026-08-16). Data as JSON: /api/errors/920948dea660b4de. Report an issue: GitHub.